Planar filament with focused, central electron emission

Abstract

A planar filament for an x-ray tube can have a different cross-sectional area at different locations. In regions of smaller cross-sectional area, there can be higher current density, and thus increased heating and higher temperature of the wire. In regions of larger cross-sectional area, there can be lower current density, and thus decreased heating of the wire. Regions of larger cross-sectional area can also be stronger, thus reducing early filament failures. Wider regions can have increased area for electron emission. By adjusting the cross-sectional area and width of the wire at different locations, electron emission can be largely confined to a center of the filament, and filament life can increase.

What is claimed is: 
     
       1. An x-ray tube comprising:
 a cathode and an anode electrically insulated from one another, the cathode including a filament configured to emit electrons towards the anode, and the anode configured to emit x-rays out of the x-ray tube in response to impinging electrons from the filament; 
 the filament comprises an elongated wire extending non-linearly in a plane between a pair of electrodes, the filament capable of being heated by an electrical current through the elongated wire due to a voltage differential across the pair of electrodes; 
 the filament includes a spiral segment with the elongated wire forming at least one complete revolution about an axis at a center of the filament, the filament forming a double spiral shape oriented parallel to the plane; 
 the filament includes a pair of low-regions, a pair of outer-high-regions, and a central-high-region; 
 each low-region is electrically-coupled to one of the outer-high-regions at one end and to the central-high-region at an opposite end; 
 the low-regions and the central-high-region are electrically-coupled between the pair of outer-high-regions; and 
 each low-region is configured to have lower current density, due to a larger cross-sectional area of the wire in the low-region, than a current density of the outer-high-region adjacent to the low-region and a current density of the central-high-region adjacent to the low-region. 
 
     
     
       2. The x-ray tube of  claim 1 , wherein A 12 /A 11 ≥1.1 and A 12 /A 13 ≥1.1, where A 12  is the cross-sectional area of the wire of each low-region, A 11  is the cross-sectional area of the wire of the outer-high-region adjacent to the low-region, and A 13  is the cross-sectional area of the wire of the central-high-region. 
     
     
       3. The x-ray tube of  claim 1 , wherein each low-region has at least 15% less current density during operation as in the central-high-region and in the outer-high-region adjacent to the low-region. 
     
     
       4. The x-ray tube of  claim 1 , wherein a width of the wire in each low-region is larger than a width of the wire in the outer-high-region adjacent to the low-region and larger than a width of the wire in the central-high-region. 
     
     
       5. The x-ray tube of  claim 1 , wherein W 12 /W 11 ≥1.1 and W 12 /W 13 ≥1.1, where W 12  is a width of the wire in each low-region, W 11  is a width of the wire in the outer-high-region adjacent to the low-region, and W 13  is a width of the wire in the central-high-region. 
     
     
       6. The x-ray tube of  claim 1 , wherein a thickness of the wire in each low-region is larger than a thickness of the wire in the outer-high-region adjacent to the low-region and larger than a thickness of the wire in the central-high-region. 
     
     
       7. The x-ray tube of  claim 1 , wherein T 12 /T 11 ≥1.1 and T 12 /T 13 ≥1.1, where T 12  is a thickness of the wire in each low-region, T 11  is a thickness of the wire in the outer-high-region adjacent to the low-region, and T 13  is a thickness of the wire in the central-high-region. 
     
     
       8. An x-ray tube comprising:
 a cathode and an anode electrically insulated from one another, the cathode including a filament configured to emit electrons towards the anode, and the anode configured to emit x-rays out of the x-ray tube in response to impinging electrons from the filament; 
 the filament comprises an elongated wire extending non-linearly in a plane between a pair of electrodes, the filament capable of being heated by an electrical current through the elongated wire due to a voltage differential across the pair of electrodes; 
 the filament includes a spiral segment with the elongated wire forming at least one complete revolution about an axis at a center of the filament, on either side of the axis, the filament forming a double spiral shape oriented parallel to the plane; 
 the filament includes a pair of low-regions, a pair of central-high-regions, and a center-region; 
 the center-region is located between and electrically-coupled to each of the pair of central-high-regions; 
 each central-high-region is electrically-coupled to one of the low-regions at one end and to the center-region at an opposite end; 
 each central-high-region is configured to have higher current density during operation, due to a smaller cross-sectional area of the wire in the central-high-region, than the low-region and the center-region adjacent to it. 
 
     
     
       9. The x-ray tube of  claim 8 , wherein each central-high-region has ≥1.1 times as much current density during operation as in the low-region and in the center-region adjacent to the central-high-region. 
     
     
       10. The x-ray tube of  claim 8 , wherein a thickness of the wire in each central-high-region is smaller than a thickness of the wire in the low-region adjacent to the central-high-region and smaller than a thickness of the wire in the center-region. 
     
     
       11. The x-ray tube of  claim 8 , wherein T 12 /T 13 ≥1.1 and T 14 /T 13 ≥1.1, where T 12  is a thickness of the wire in each low-region, T 13  is a thickness of the wire in the central-high-region adjacent to the low-region, and T 14  is a thickness of the wire in the center-region. 
     
     
       12. The x-ray tube of  claim 8 , wherein a junction between each low-region and the central-high-region adjacent to the low-region is located in a central 25% of a length of the wire. 
     
     
       13. The x-ray tube of  claim 8 , wherein the pair of low-regions are located in a central 25% of a length of the wire. 
     
     
       14. The x-ray tube of  claim 8 , wherein the center-region is located at a center of the filament.